Africa Water, Sanitation & Hygiene September 2018 Vol.13 No.4 | Page 11

NEWS in brief
Global Highlights
“We are surprised by the Pakistani results,” says
Kedar Nath Ghimire, a chemistry researcher
at Tribhuvan University, Kathmandu, who
experimented with sugarcane bagasse. “Our studies
demonstrated that such material removed heavy
transition metals but not arsenic,” he told SciDev.
Net.
This article was produced by SciDev.Net’s Asia & Pacific
desk.
Wastewater Recycling Instead of Disposal
Wastewater smells foul and is full of pathogens
so it is usually removed and disposed. The out-of-
sight-out-of-mind strategy is, however, costly and
opportunities are lost. At Eawag’s Info Day, experts
in practice come together with researchers who
are seeking new answers – for example, on how
nutrients or heat can be recovered from wastewater.
Switzerland is rightly proud of its wastewater treatment
strategy. It guarantees hygiene in communities, protects
water as a resource (eg. for drinking water) and successfully
prevents over-fertilization of rivers and lakes. But this
comes at a price: the replacement value of the Swiss
wastewater infrastructure amounts to more than 120
billion francs.
New challenges, for example the removal of
micropollutants or climate change, are not make the
system less costly. In addition, it is becoming ever clearer
that wastewater is not simply a hazard to be removed, but
it also embodies resources such as heat or nutrients that
it would be more sensible to recycle instead of literally
flushing them away.
How these materials can best be recovered, as well as the
limits of this recycling, is the topic of discussion today at
the Eawag Info Day in Dübendorf among ca. 200 experts
from scientific fields, administration, policy and practice.
They are focusing on the topic “Wastewater as a resource”
and will be exchanging knowledge about future-oriented
technologies for the recovery of valuable resources from
the unpleasant brown brew. More info available in the
Tagungsband (pdf).
For example energy
Take energy, for example: there is a great deal of energy
in wastewater that was previously absorbed in the water
for hot showers or washing. In new buildings today, this is
the major source of energy leakage. In both decentralised
situations, before it leaves the building, and centralised –
for example in a main collecting channel – such energy
can be partially recovered. The fact that the wastewater is
then somewhat cooler is, in addition, an advantage in these
days of ever-warmer brooks and rivers. Such recovery
installations have to be planned early on, otherwise other
energy sources have an advantage.
Energy is also present in faeces, which contain a lot of
carbon. An Eawag project shows how in countries in the
global south, pellets are manufactured from faecal sludge
and used for heating the kilns used in tile manufacture. The
advantage of this concept is that it can become a small
business for entrepreneurs, with the view to operating
long term. Electricity can be produced from wastewater
with ever-greater efficiency via gas from purification
plants, produced in anaerobic degradation processes. As
wastewater treatment plants thus become energy suppliers,
their providers in a liberalised market are suddenly faced
with new questions, such as When would the recovered
energy be better used at source and when should it be sold
for profit?
Costs and values - two different things
Wastewater recycling sounds good, but opportunities and
costs have to be realistically evaluated. The total wastewater
disposal in Switzerland costs c. 300 francs per resident per
year. By contrast, electricity can be produced from sewage
sludge for around three francs per head, and the phosphate
in wastewater is currently valued at around one franc per
head of the population at world market prices. No one, in
other words, will get rich from this practice.
Only when the whole picture is examined, and priorities
supported by society are set, does the balance sheet start
to look better. A switch from the present wastewater
disposal to modern wastewater recycling keeps damaging
micropollutants out of the most diverse waters and avoids
the emission of greenhouse gases. In areas where water
is scarce, it can be worthwhile to produce drinking water
from wastewater, and innovative fertilizer production
in treatment plants can lead to new opportunities in
agriculture. This is not easily expressed in tons or francs,
but must be part of the cost/income equation.
Source: EAWAG
Africa Water, Sanitation & Hygiene • August 2018
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